NZ Landscaper Magazine
TIMBER DECKS CONTINUED
When cutting directly over the centre of a joist, care must be taken to avoid nails or screws from the original installation. If it is too difficult to remove the section of the board over the joist without damaging the saw, cut the board at the edge of the joist. Nail a block to the side of the joist to provide a nailing surface for the new board to be installed
(see Figure 1).
IMPROVING DECK DRAINAGE
Rot to decking timber, joists or wall cladding is likely to be due to poor drainage where components intersect such as between decking and wall cladding, decking and joists or wall cladding and stringer.
Between decking and wall cladding
To improve the drainage between decking and wall cladding, create a gap between the decking and the cladding:
• Remove the decking board closest to the wall cladding and cut a minimum 12mm piece off the edge of the board. • Replace the board leaving a 12mm gap between the edge of the board and the cladding. • If the existing board cannot be reused, replace it with a matching decking timber (minimum H3.2) leaving a 12mm gap between the edge of the board and the cladding.
Between decking and joists
Insufficient drainage between the decking timber and the top of the joists may be because the decking timbers do not have enough gap between adjacent boards, restricting free drainage.
The only way to fix this problem is to remove and replace the decking timbers. Reinstall the reused or new decking boards allowing a 3–6mm gap between boards for drainage.
Between wall cladding and stringer
If there is rot in either the cladding and/or the stringer where they abut, there may be no gap to allow water to drain away. Create a gap between the cladding and the stringer:
• Install a temporary bearer under the floor joists close to the stringer and supported with hydraulic jacks. The temporary bearer should be at least the same depth as the stringer. • Slowly jack up the temporary bearer by raising each jack approximately 5mm in turn until the bearer has been raised enough to remove the load from the stringer and provide access to cut through joist fastenings. • Cut through nails fixing joists to the stringer using a hacksaw. • Unfasten the bolts attaching the stringer to the wall and remove the stringer.
• If there is rot in the weatherboards, the affected boards will need to be replaced – refer to BRANZ Good Repair Guide Horizontal timber weatherboards.
• Insert H3.2 treated, 150 × 12mm thick packers (or UV-resistant 12mm plastic washers) with holes the same diameter as the bolt fixings at each bolt fixing.
• If the stringer can be reused, rebolt the stringer to the wall over the packers.
• If the stringer cannot be reused, fix a new stringer to the wall over the packers.
The stringer should be H3.2 treated timber and either
190 × 45mm or 140 × 45mm depending on joist spans and bolt spacings. See
NZS 3604:2011 Timber-framed buildings section 6.13.
• Refasten the joists to the stringer.
• Remove the jacks and temporary beam. See Figure 2.
REPLACING CORRODED FIXINGS
Fixings that have corroded lose strength and should be replaced.
Corrosion may also cause staining of timber around the nails. While this is not a structural problem, if visually unacceptable, the staining can only be removed by replacing boards.
EXTENSIVE REPAIR WORK SUCH AS DECK REPLACEMENT
If decking timber is in poor condition generally, the best solution may be to remove and replace it. Grooved or ridged decking timber should be laid with the grooved side down so that air can circulate where the boards are in contact with the joists.